The present invention relates to implantable medical devices. In particular, the present invention relates to a charging of a storage capacitor from a battery and subsequently delivering stored energy from the storage capacitor to a pump motor.
Implantable drug delivery devices are used to provide patients with long-term dosage or infusion of a drug or other therapeutic agent. Implantable drug delivery devices may be categorized as either passive or active devices.
Passive drug delivery devices typically rely upon a pressurized drug reservoir to deliver the drug. The reservoir may be filled using a syringe. The drug is then delivered to the patient using force provided by the pressurized reservoir.
Active drug delivery devices include a pump or metering system to deliver the drug into the patient's system. The pump is electrically powered to deliver the drug from a reservoir through a catheter to a selected location within the patient's body. The pump typically includes a battery as its power source for both the pump and for the electronic circuitry used to control flow rate of the pump and to communicate through telemetry to an external device to allow programming of the pump.
Battery life is an important consideration for all implantable medical devices. With an implantable drug delivery device, efficiency of the driver circuitry that powers the pump motor is an important consideration. In one type of driver configuration, the pump motor is driven from electrical energy stored by a storage capacitor. The capacitor serves as a low-impedance, short-term energy reservoir to deliver sufficient power to the motor during assertion. During operation, the motor will be asserted periodically for a short period of time to provide a pulse flow of the drug, with longer period until the next assertion.
The efficiency of the driver circuitry can have an important effect on the lifetime of the battery, overall volume of the device including battery size, capacitor size, and size of the circuitry required, and on the overall cost of the device. Considerations in the efficiency of the driver include efficiency of charging the storage capacitor, and efficiency of delivering energy stored in the storage capacitor to the pump motor.